1. Field of the Invention
The present invention relates to a golf ball providing superior hit feel, large ball flight distances (impact resilience), superior spin characteristics (controllability), and superior abrasion resistance.
2. Description of the Related Art
Golf balls providing large ball flight distances and high spinning performance in approach shots have been proposed to have a center core of soft rubber, an intermediate layer overlying and covering the core and formed of relatively hard rubber, and a cover thereon formed of soft material to allow the golf balls to have a dual-layer core or a dual-layer cover structure.
For example, U.S. Pat. No. 5,553,852 discloses a golf ball having a center core of having a diameter of no less than 29 mm, and an intermediate layer having a JIS-C hardness of no less than 85, with the center core greater in specific gravity than the intermediate layer. The intermediate layer, however, is formed of ionomer and the golf ball thus provides a small coefficient of restitution and thus cannot provide large ball flight distances.
U.S. Pat. No. 5,899,822 discloses a golf ball having a solid core with a deformability of no less than 2.5 mm for a load of 100 kg, and an intermediate layer harder than the cover by a Shore-D of no less than 13, with a moment of inertia of no less than 83 g cm2. The cover, however, is formed of urethane resin and the golf ball thus provides a small coefficient of restitution and thus cannot provide large ball flight distances.
Furthermore, U.S. Pat. No. 6,248,029 discloses a multi-piece golf ball having a solid core formed of inner and outer cores, and an intermediate layer outer than the solid core, wherein the solid core and the intermediate layer is formed of a rubber composite containing polybutadiene as a main component and the inner core has a diameter of 15 to 22 mm and a Shore-D hardness of 40 to 70. However, the diameter of the inner core is too small and the golf ball thus provides a small coefficient of restitution and it also has a large spin rate at impact and thus cannot provide large ball flight distances when it is hit with a driver.
Using various types of soft material for covers has also been proposed. For example, U.S. Pat. No. 4,884,814 discloses using soft ionomer resin to form a cover. More specifically, ethylene-(meth)acryl acid-(meth)acrylate ester terpolymer, a relatively soft ionomer resin, blended with ionomer resin of ethylene-(meth)acryl acid copolymer of a physical property extent to an extent is used to provide a cover of a blend of soft and hard ionomers. This technique improves the inferior hit feel and poor controllability of conventional golf balls having a cover of ionomer resin of ethylene-(meth)acryl acid copolymer.
However, the cover of the blend of soft and hard ionomers is soft, which helps to increase spin rate for ion shot, while it increases friction between a club face and the cover and in particular when a two-piece solid golf ball or any other similar golf ball having a hard core member is hit with an iron club the grooves of the iron club abrade the cover surface and the ball would thus have a rough surface. This ionomer cover has a low level of hardness and the cover itself has small impact resilience resulting in the exact ball having small impact resilience.
Accordingly GB 2264302 proposes using a metallic salt of ethylene-unsaturated carboxylic acid-unsaturated carboxylate terpolymer having at least two types of low bending moduli to form a cover of a golf ball to reduce abrasion of the cover of the golf ball hit with an iron club. However, when the ball with the cover thus produced is hit with an iron club it exhibits insufficient abrasion resistance and also reduces in impact resilience.
Furthermore, Japanese Patent Laying-open No. 10-179802 proposes a golf ball having a cover with a base material of resin containing two components, ionomer resin and an epoxy group containing, stylene-butadiene-stylene block copolymer or an epoxy group containing, stylene-isoprene-stylene block copolymer, heated and mixed together, as main components, the cover being of a composite providing a flexural rigidity of 50 to 300 MPa, with a Shore-D hardness of 40 to 60.
Furthermore, GB 2311530 proposes a golf ball having a cover with a base resin containing three components, ionomer resin, an acid-modified, thermoplastic elastomer or a thermoplastic elastomer having a terminal with OH group added thereto, and an epoxy group containing, stylene-butadiene-stylene block copolymer or an epoxy group containing, stylene-isoprene-stylene block copolymer, heated and mixed together, as main components, the cover being of a composite providing a flexural rigidity of 50 to 300 MPa, with a Shore D hardness of 40 to 60.
These inventions do improve hit feel, spin characteristics (controllability) and cut resistance, although they do not provide sufficient ball flight distances
The present invention provides a golf ball providing superior hit feel, large ball flight distances, superior spin characteristics (controllability), and superior abrasion resistance for the golf ball hit with an iron club.
The present golf ball includes a center core, an intermediate layer and a cover, wherein:
the center core has a diameter of 25 to 40 mm, and a surface hardness (B) and a center hardness (A), the surface hardness (B) being at least 15 greater than the center hardness (A), as measured in Shore D hardness;
the intermediate layer has a surface hardness (C) 20 to 50 greater than the center hardness (A) of the center core, as measured in Shore D hardness;
the cover has a hardness (D) of 40 to 60, as measured in Shore D hardness; and
the surface hardness (C) of the intermediate layer is 5 to 25 greater than the hardness (D) of the cover, as measured in Shore D hardness. Preferably the center core and the intermediate layer are formed of a rubber composite containing cis-1, 4 polybutadiene rubber as a main component.
Furthermore in the present invention desirably a cover composite contains a polymer component containing 10 to 80 parts by weight of ethylene-(meth)acrylic acid copolymer-type ionomer resin (a component A), 0 to 60 parts by weight of ethylene-(meth)acrylic acid-(meth)acrylic ester terpolymer-type ionomer resin (a component B), and 5 to 60 parts by weight of a styrene block containing, thermoplastic elastomer (a component C).
Preferably the styrene block containing, thermoplastic elastomer (the component C) is a polymer alloy of a styrene-butadiene-styrene block copolymer (SBS), a styrene-isoprene-styrene block copolymer (SIS), a styrene-isoprene-butadiene-styrene block copolymer (SIBS) or a hydrogenation thereof and olefin. In the present invention desirably the intermediate layer is greater in specific gravity than the center core.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.